134 SOCIAL HABITATIONS. 
regular increase in diameter. At their origin, they are so 
small that the finest thread could hardly pass through 
them, but in proportion as they increase in length they 
increase in width, so that at their termination they are 
sometimes the twelfth of an inch in width. 
These marks are the tracks made by very small larvee, 
which live between the membranes of the leaves, and 
feed upon the parenchyma, or soft substance which lies 
between the two membranes. They follow no rule in 
their meanderings, but traverse the leaf in a variety of 
ways. Sometimes they never leave the edge, but follow 
every little serration of the leaf with perfect accuracy. 
Sometimes they form a kind of spiral, and sometimes 
they wander irregularly over the whole leaf. Generally, 
the insect does not cross the track which it has once 
made, being diverted from doing so by some wonderful 
instinct. There are instances, however, where the insect 
has crossed its own track, not only once, but several 
times. 
If the little gallery be opened at the widest extremity, 
one of three things will be found. Sometimes there is 
a tiny white grub, very much resembling the larva of 
certain beetles, and having the rings which represent 
the thorax rather wider than those which will afterwards 
be developed into the abdomen. As the little creature 
is able to live between the membranes of a leaf so thin 
as that of the rose or oak, it is evident, to the most 
superficial observer, that the insect which will be de- 
veloped from it must be of very minute dimensions. 
The larva of all winged insects is very large in pro- 
portion to the same insects when they have obtained 
their perfect form, much of the substance being taken 
up by the wings. As a natural consequence, it follows 
that the larger the wings, the larger must be the grub, 
